The control of bleeding during surgery is an important issue. Electrosurgical techniques that pass a current through the patient's tissue between two electrodes for both cutting and causing hemostasis to tissue are known. The current passing through the tissue causes heating of the tissue as a function of the current density and the resistance of the tissue. Such heating causes the tissue proteins to form coagulum that seals the bleeding sites.
In bipolar electrosurgical devices, two electrodes are closely spaced together to thereby confine current flow locally to the tissue disposed between the electrodes. One difficulty encountered with prior art electrosurgical devices is that of controlling the current flow to the patient's tissue such that no undesirable trauma is brought about in adjacent tissue. Although bipolar electrosurgical devices have helped to localize current flow, these devices have yet to be optimized in this respect. Further, some of these devices present difficulties in selectively applying the current flow.
For example, U.S. Pat. No. 3,651,811 describes bipolar electrosurgical scissors having opposing cutting blades forming active electrodes. This device enables a surgeon to sequentially coagulate the blood vessels contained in the tissue and mechanically sever the tissue with the scissor blades. However, since the blades form the electrodes, coagulation must be a separate step from cutting in order to avoid contact between two scissor blades so that they do not short circuit.
One proposed solution to this problem can be found in U.S. Pat. Nos. 5,352,222 and 5,356,408. These patents disclose bipolar electrosurgical scissors wherein each cutting blade includes a cutting surface, an electrically non-conductive layer and an electrically conductive outer surface which serves as the electrode.
However, these devices suffer from three important disadvantages. First, they require a three layer laminate which makes them difficult to manufacture. Second, the flow of electric current through the tissue is not sufficiently localized by these devices since the current must flow from the back of one cutting blade element to the back of the other cutting blade element. Finally, since the current is not applied directly via the cutting surface, this device does not optimize cutting and coagulation.
Another bipolar electrosurgical cutting apparatus is disclosed in U.S. Pat. No. 5,324,289. In one embodiment disclosed in this patent, one of the cutting surfaces is made of a conductive material and serves as an electrode while the other cutting surface is covered by a coating of a non-conductive material. Thus, in this device, the current flows from the surface of one cutting edge to the back side of the other cutting edge. Accordingly, this device suffers from the same disadvantage as the previous device in that the flow of electric current is not sufficiently localized to prevent trauma to adjacent tissue and provide optimum cutting and coagulation.
Thus, a need exists for improvements in bipolar electrosurgical instruments in order to further localize current flow, reduce manufacturing costs and improve the overall efficiency of such devices.